Characterization of soluble microbial products (SMP) under stressful conditions.

Soluble microbial products (SMP) in the wastewater treatment process not only cause fouling to the membrane, but also generate disinfection by-products (DBP) in the effluent, thus get increasing attention. In this study, SMP produced by activated sludge and isolates under different stressful conditions, i.e. starvation, salinity, heavy metals, low pH and high temperature, were characterized to investigate the effects of these conditions on the amount of SMP and their compositions. The analysis results using size exclusion chromatography (SEC), high pressure liquid chromatography (HPLC) and fluorescence excitation emission matrix (FEEM) showed that activated sludge and isolates suffered with the same stressful condition contained almost the same concentration and composition of SMP, indicating that the stressful condition instead of the microbial species played the crucial role in the production of SMP. Among of stressful conditions tested, high temperature had stimulated the production of polysaccharides and polycarboxylate-type humic acid with high hydrophilicity, which is in positive proportion to the foulants formation potential, thus should be avoided in membrane bioreactors. Low pH had promoted the generation of hydrophobic humic acid-like or protein-like organics, which had been proved as the main disinfection byproduct (DBP) precursor, thus should be avoided in the biological treatment. Starvation had less effect on SMP production as the seeding microbes had no substrates.